Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.98   8.570%   $222.5468   $222.55   $222.55   $222.50  
  Purchase #2 $101.59   9.219%   $110.9556   $110.96   $110.95   $111.00  
  Purchase #3 $243.77   8.256%   $263.8957   $263.90   $263.90   $263.90  
  Purchase #4 $140.92   8.303%   $152.6206   $152.62   $152.60   $152.60  
  Purchase #5 $238.54   5.668%   $252.0604   $252.06   $252.05   $252.10  
  Purchase #6 $122.97   8.332%   $133.2159   $133.22   $133.20   $133.20  
  Purchase #7 $210.51   13.594%   $239.1267   $239.13   $239.15   $239.10  
  7 purchase totals = $1,263.28       $1,374.4217   $1,374.44   $1,374.40   $1,374.40