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 $59.74   8.782%   $64.9864   $64.99   $65.00   $65.00  
  Purchase #2 $165.61   8.750%   $180.1009   $180.10   $180.10   $180.10  
  Purchase #3 $108.60   8.690%   $118.0373   $118.04   $118.05   $118.00  
  Purchase #4 $129.37   13.128%   $146.3537   $146.35   $146.35   $146.40  
  Purchase #5 $142.47   13.375%   $161.5254   $161.53   $161.55   $161.50  
  Purchase #6 $74.25   3.245%   $76.6594   $76.66   $76.65   $76.70  
  Purchase #7 $156.54   9.436%   $171.3111   $171.31   $171.30   $171.30  
  7 purchase totals = $836.58       $918.9742   $918.98   $919.00   $919.00