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 $46.50   3.702%   $48.2214   $48.22   $48.20   $48.20  
  Purchase #2 $47.58   8.293%   $51.5258   $51.53   $51.55   $51.50  
  Purchase #3 $182.32   11.340%   $202.9951   $203.00   $203.00   $203.00  
  Purchase #4 $165.63   3.553%   $171.5148   $171.51   $171.50   $171.50  
  Purchase #5 $163.92   9.308%   $179.1777   $179.18   $179.20   $179.20  
  Purchase #6 $243.58   11.453%   $271.4772   $271.48   $271.50   $271.50  
  Purchase #7 $99.52   5.173%   $104.6682   $104.67   $104.65   $104.70  
  7 purchase totals = $949.05       $1,029.5802   $1,029.59   $1,029.60   $1,029.60