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 $232.55   13.676%   $264.3535   $264.35   $264.35   $264.40  
  Purchase #2 $227.58   13.624%   $258.5855   $258.59   $258.60   $258.60  
  Purchase #3 $232.52   13.618%   $264.1846   $264.18   $264.20   $264.20  
  Purchase #4 $130.99   5.336%   $137.9796   $137.98   $138.00   $138.00  
  Purchase #5 $126.75   4.376%   $132.2966   $132.30   $132.30   $132.30  
  Purchase #6 $201.46   8.372%   $218.3262   $218.33   $218.35   $218.30  
  Purchase #7 $41.70   10.801%   $46.204   $46.20   $46.20   $46.20  
  7 purchase totals = $1,193.55       $1,321.9300   $1,321.93   $1,322.00   $1,322.00