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 $122.26   6.486%   $130.1898   $130.19   $130.20   $130.20  
  Purchase #2 $226.92   3.562%   $235.0029   $235.00   $235.00   $235.00  
  Purchase #3 $94.66   7.679%   $101.9289   $101.93   $101.95   $101.90  
  Purchase #4 $191.66   3.130%   $197.659   $197.66   $197.65   $197.70  
  Purchase #5 $70.50   6.685%   $75.2129   $75.21   $75.20   $75.20  
  Purchase #6 $110.92   6.594%   $118.2341   $118.23   $118.25   $118.20  
  Purchase #7 $26.56   6.564%   $28.3034   $28.30   $28.30   $28.30  
  7 purchase totals = $843.48       $886.5310   $886.52   $886.55   $886.50