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 $228.98   10.807%   $253.7259   $253.73   $253.75   $253.70  
  Purchase #2 $23.59   11.605%   $26.3276   $26.33   $26.35   $26.30  
  Purchase #3 $123.68   8.828%   $134.5985   $134.60   $134.60   $134.60  
  Purchase #4 $17.42   6.606%   $18.5708   $18.57   $18.55   $18.60  
  Purchase #5 $160.68   8.453%   $174.2623   $174.26   $174.25   $174.30  
  Purchase #6 $227.26   6.392%   $241.7865   $241.79   $241.80   $241.80  
  Purchase #7 $211.96   5.319%   $223.2342   $223.23   $223.25   $223.20  
  7 purchase totals = $993.57       $1,072.5058   $1,072.51   $1,072.55   $1,072.50