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 $214.45   12.249%   $240.718   $240.72   $240.70   $240.70  
  Purchase #2 $181.90   11.412%   $202.6584   $202.66   $202.65   $202.70  
  Purchase #3 $58.33   7.162%   $62.5076   $62.51   $62.50   $62.50  
  Purchase #4 $204.47   6.683%   $218.1347   $218.13   $218.15   $218.10  
  Purchase #5 $156.48   6.843%   $167.1879   $167.19   $167.20   $167.20  
  Purchase #6 $42.65   5.534%   $45.0103   $45.01   $45.00   $45.00  
  Purchase #7 $197.83   8.741%   $215.1223   $215.12   $215.10   $215.10  
  7 purchase totals = $1,056.11       $1,151.3392   $1,151.34   $1,151.30   $1,151.30