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 $62.44   7.710%   $67.2541   $67.25   $67.25   $67.30  
  Purchase #2 $230.56   10.522%   $254.8195   $254.82   $254.80   $254.80  
  Purchase #3 $23.49   9.562%   $25.7361   $25.74   $25.75   $25.70  
  Purchase #4 $162.81   11.364%   $181.3117   $181.31   $181.30   $181.30  
  Purchase #5 $58.32   8.324%   $63.1746   $63.17   $63.15   $63.20  
  Purchase #6 $152.95   4.502%   $159.8358   $159.84   $159.85   $159.80  
  Purchase #7 $208.70   7.333%   $224.004   $224.00   $224.00   $224.00  
  7 purchase totals = $899.27       $976.1358   $976.13   $976.10   $976.10