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 $178.80   8.525%   $194.0427   $194.04   $194.05   $194.00  
  Purchase #2 $85.36   10.661%   $94.4602   $94.46   $94.45   $94.50  
  Purchase #3 $177.29   3.530%   $183.5483   $183.55   $183.55   $183.50  
  Purchase #4 $150.49   3.511%   $155.7737   $155.77   $155.75   $155.80  
  Purchase #5 $167.36   11.586%   $186.7503   $186.75   $186.75   $186.80  
  Purchase #6 $81.63   11.663%   $91.1505   $91.15   $91.15   $91.20  
  Purchase #7 $99.52   5.369%   $104.8632   $104.86   $104.85   $104.90  
  7 purchase totals = $940.45       $1,010.5889   $1,010.58   $1,010.55   $1,010.70