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 $54.56   13.161%   $61.7406   $61.74   $61.75   $61.70  
  Purchase #2 $198.99   10.373%   $219.6312   $219.63   $219.65   $219.60  
  Purchase #3 $203.65   11.801%   $227.6827   $227.68   $227.70   $227.70  
  Purchase #4 $216.47   9.568%   $237.1818   $237.18   $237.20   $237.20  
  Purchase #5 $40.84   8.362%   $44.255   $44.26   $44.25   $44.30  
  Purchase #6 $248.52   6.229%   $264.0003   $264.00   $264.00   $264.00  
  Purchase #7 $10.95   6.546%   $11.6668   $11.67   $11.65   $11.70  
  7 purchase totals = $973.98       $1,066.1584   $1,066.16   $1,066.20   $1,066.20