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 $181.92   6.362%   $193.4938   $193.49   $193.50   $193.50  
  Purchase #2 $204.67   11.237%   $227.6688   $227.67   $227.65   $227.70  
  Purchase #3 $35.52   9.359%   $38.8443   $38.84   $38.85   $38.80  
  Purchase #4 $58.26   13.280%   $65.9969   $66.00   $66.00   $66.00  
  Purchase #5 $225.61   13.554%   $256.1892   $256.19   $256.20   $256.20  
  Purchase #6 $247.58   8.566%   $268.7877   $268.79   $268.80   $268.80  
  Purchase #7 $69.84   9.647%   $76.5775   $76.58   $76.60   $76.60  
  7 purchase totals = $1,023.40       $1,127.5582   $1,127.56   $1,127.60   $1,127.60