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 $188.86   11.851%   $211.2418   $211.24   $211.25   $211.20  
  Purchase #2 $148.63   13.487%   $168.6757   $168.68   $168.70   $168.70  
  Purchase #3 $159.27   9.279%   $174.0487   $174.05   $174.05   $174.00  
  Purchase #4 $48.53   11.732%   $54.2235   $54.22   $54.20   $54.20  
  Purchase #5 $184.89   13.456%   $209.7688   $209.77   $209.75   $209.80  
  Purchase #6 $203.33   13.304%   $230.381   $230.38   $230.40   $230.40  
  Purchase #7 $52.60   11.678%   $58.7426   $58.74   $58.75   $58.70  
  7 purchase totals = $986.11       $1,107.0821   $1,107.08   $1,107.10   $1,107.00