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 $92.76   6.706%   $98.9805   $98.98   $99.00   $99.00  
  Purchase #2 $176.28   7.301%   $189.1502   $189.15   $189.15   $189.20  
  Purchase #3 $235.74   13.288%   $267.0651   $267.07   $267.05   $267.10  
  Purchase #4 $91.80   3.785%   $95.2746   $95.27   $95.25   $95.30  
  Purchase #5 $66.93   12.551%   $75.3304   $75.33   $75.35   $75.30  
  Purchase #6 $66.82   7.756%   $72.0026   $72.00   $72.00   $72.00  
  Purchase #7 $54.42   3.245%   $56.1859   $56.19   $56.20   $56.20  
  7 purchase totals = $784.75       $853.9893   $853.99   $854.00   $854.10