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 $50.31   7.252%   $53.9585   $53.96   $53.95   $54.00  
  Purchase #2 $103.30   10.596%   $114.2457   $114.25   $114.25   $114.20  
  Purchase #3 $196.53   3.616%   $203.6365   $203.64   $203.65   $203.60  
  Purchase #4 $25.96   11.791%   $29.0209   $29.02   $29.00   $29.00  
  Purchase #5 $226.71   13.372%   $257.0257   $257.03   $257.05   $257.00  
  Purchase #6 $173.69   13.742%   $197.5585   $197.56   $197.55   $197.60  
  Purchase #7 $170.29   5.499%   $179.6542   $179.65   $179.65   $179.70  
  7 purchase totals = $946.79       $1,035.1000   $1,035.11   $1,035.10   $1,035.10