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 $200.77   3.477%   $207.7508   $207.75   $207.75   $207.80  
  Purchase #2 $194.31   7.471%   $208.8269   $208.83   $208.85   $208.80  
  Purchase #3 $114.92   13.665%   $130.6238   $130.62   $130.60   $130.60  
  Purchase #4 $186.29   11.190%   $207.1359   $207.14   $207.15   $207.10  
  Purchase #5 $169.79   5.293%   $178.777   $178.78   $178.80   $178.80  
  Purchase #6 $34.77   12.116%   $38.9827   $38.98   $39.00   $39.00  
  Purchase #7 $77.34   13.678%   $87.9186   $87.92   $87.90   $87.90  
  7 purchase totals = $978.19       $1,060.0157   $1,060.02   $1,060.05   $1,060.00