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 $85.46   7.606%   $91.9601   $91.96   $91.95   $92.00  
  Purchase #2 $49.67   11.124%   $55.1953   $55.20   $55.20   $55.20  
  Purchase #3 $7.39   3.347%   $7.6373   $7.64   $7.65   $7.60  
  Purchase #4 $90.29   13.606%   $102.5749   $102.57   $102.55   $102.60  
  Purchase #5 $75.57   11.606%   $84.3407   $84.34   $84.35   $84.30  
  Purchase #6 $65.50   8.434%   $71.0243   $71.02   $71.00   $71.00  
  Purchase #7 $63.36   11.236%   $70.4791   $70.48   $70.50   $70.50  
  7 purchase totals = $437.24       $483.2117   $483.21   $483.20   $483.20