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 $143.77   7.360%   $154.3515   $154.35   $154.35   $154.40  
  Purchase #2 $205.49   8.357%   $222.6628   $222.66   $222.65   $222.70  
  Purchase #3 $182.33   3.546%   $188.7954   $188.80   $188.80   $188.80  
  Purchase #4 $76.33   13.142%   $86.3613   $86.36   $86.35   $86.40  
  Purchase #5 $219.79   11.560%   $245.1977   $245.20   $245.20   $245.20  
  Purchase #6 $123.49   9.635%   $135.3883   $135.39   $135.40   $135.40  
  Purchase #7 $25.38   7.479%   $27.2782   $27.28   $27.30   $27.30  
  7 purchase totals = $976.58       $1,060.0352   $1,060.04   $1,060.05   $1,060.20