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 $83.48   3.428%   $86.3417   $86.34   $86.35   $86.30  
  Purchase #2 $95.38   11.152%   $106.0168   $106.02   $106.00   $106.00  
  Purchase #3 $202.58   9.601%   $222.0297   $222.03   $222.05   $222.00  
  Purchase #4 $89.85   3.873%   $93.3299   $93.33   $93.35   $93.30  
  Purchase #5 $102.49   8.751%   $111.4589   $111.46   $111.45   $111.50  
  Purchase #6 $62.31   3.671%   $64.5974   $64.60   $64.60   $64.60  
  Purchase #7 $197.56   13.782%   $224.7877   $224.79   $224.80   $224.80  
  7 purchase totals = $833.65       $908.5621   $908.57   $908.60   $908.50