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 $151.96   11.457%   $169.3701   $169.37   $169.35   $169.40  
  Purchase #2 $84.29   8.349%   $91.3274   $91.33   $91.35   $91.30  
  Purchase #3 $122.90   3.765%   $127.5272   $127.53   $127.55   $127.50  
  Purchase #4 $184.25   10.280%   $203.1909   $203.19   $203.20   $203.20  
  Purchase #5 $37.97   13.312%   $43.0246   $43.02   $43.00   $43.00  
  Purchase #6 $64.62   5.516%   $68.1844   $68.18   $68.20   $68.20  
  Purchase #7 $211.53   8.690%   $229.912   $229.91   $229.90   $229.90  
  7 purchase totals = $857.52       $932.5366   $932.53   $932.55   $932.50