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 $174.95   11.224%   $194.5864   $194.59   $194.60   $194.60  
  Purchase #2 $207.52   13.729%   $236.0104   $236.01   $236.00   $236.00  
  Purchase #3 $87.60   12.598%   $98.6358   $98.64   $98.65   $98.60  
  Purchase #4 $32.45   3.369%   $33.5432   $33.54   $33.55   $33.50  
  Purchase #5 $62.69   6.237%   $66.6   $66.60   $66.60   $66.60  
  Purchase #6 $28.82   11.703%   $32.1928   $32.19   $32.20   $32.20  
  Purchase #7 $136.30   6.613%   $145.3135   $145.31   $145.30   $145.30  
  7 purchase totals = $730.33       $806.8821   $806.88   $806.90   $806.80