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 $118.89   6.407%   $126.5073   $126.51   $126.50   $126.50  
  Purchase #2 $213.92   9.702%   $234.6745   $234.67   $234.65   $234.70  
  Purchase #3 $218.28   7.696%   $235.0788   $235.08   $235.10   $235.10  
  Purchase #4 $85.52   3.800%   $88.7698   $88.77   $88.75   $88.80  
  Purchase #5 $191.94   9.654%   $210.4699   $210.47   $210.45   $210.50  
  Purchase #6 $194.81   4.574%   $203.7206   $203.72   $203.70   $203.70  
  Purchase #7 $138.30   8.306%   $149.7872   $149.79   $149.80   $149.80  
  7 purchase totals = $1,161.66       $1,249.0081   $1,249.01   $1,248.95   $1,249.10