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 $180.38   12.562%   $203.0393   $203.04   $203.05   $203.00  
  Purchase #2 $96.31   8.635%   $104.6264   $104.63   $104.65   $104.60  
  Purchase #3 $172.99   11.773%   $193.3561   $193.36   $193.35   $193.40  
  Purchase #4 $15.71   5.850%   $16.629   $16.63   $16.65   $16.60  
  Purchase #5 $75.33   9.542%   $82.518   $82.52   $82.50   $82.50  
  Purchase #6 $208.30   7.201%   $223.2997   $223.30   $223.30   $223.30  
  Purchase #7 $214.69   6.344%   $228.3099   $228.31   $228.30   $228.30  
  7 purchase totals = $963.71       $1,051.7784   $1,051.79   $1,051.80   $1,051.70