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 $59.37   12.603%   $66.8524   $66.85   $66.85   $66.90  
  Purchase #2 $94.93   3.352%   $98.1121   $98.11   $98.10   $98.10  
  Purchase #3 $196.74   8.121%   $212.7173   $212.72   $212.70   $212.70  
  Purchase #4 $149.43   6.174%   $158.6558   $158.66   $158.65   $158.70  
  Purchase #5 $192.30   5.323%   $202.5361   $202.54   $202.55   $202.50  
  Purchase #6 $23.35   10.350%   $25.7667   $25.77   $25.75   $25.80  
  Purchase #7 $225.67   7.229%   $241.9837   $241.98   $242.00   $242.00  
  7 purchase totals = $941.79       $1,006.6241   $1,006.63   $1,006.60   $1,006.70