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 $87.68   7.870%   $94.5804   $94.58   $94.60   $94.60  
  Purchase #2 $181.87   9.168%   $198.5438   $198.54   $198.55   $198.50  
  Purchase #3 $24.87   11.163%   $27.6462   $27.65   $27.65   $27.60  
  Purchase #4 $223.61   7.685%   $240.7944   $240.79   $240.80   $240.80  
  Purchase #5 $180.81   9.464%   $197.9219   $197.92   $197.90   $197.90  
  Purchase #6 $225.28   5.704%   $238.13   $238.13   $238.15   $238.10  
  Purchase #7 $110.73   11.260%   $123.1982   $123.20   $123.20   $123.20  
  7 purchase totals = $1,034.85       $1,120.8149   $1,120.81   $1,120.85   $1,120.70