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 $158.26   5.541%   $167.0292   $167.03   $167.05   $167.00  
  Purchase #2 $64.78   5.787%   $68.5288   $68.53   $68.55   $68.50  
  Purchase #3 $186.98   8.700%   $203.2473   $203.25   $203.25   $203.20  
  Purchase #4 $143.56   7.180%   $153.8676   $153.87   $153.85   $153.90  
  Purchase #5 $103.98   13.667%   $118.1909   $118.19   $118.20   $118.20  
  Purchase #6 $237.73   8.323%   $257.5163   $257.52   $257.50   $257.50  
  Purchase #7 $246.34   9.160%   $268.9047   $268.90   $268.90   $268.90  
  7 purchase totals = $1,141.63       $1,237.2848   $1,237.29   $1,237.30   $1,237.20