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 $210.81   7.169%   $225.923   $225.92   $225.90   $225.90  
  Purchase #2 $67.96   5.429%   $71.6495   $71.65   $71.65   $71.60  
  Purchase #3 $75.63   7.278%   $81.1344   $81.13   $81.15   $81.10  
  Purchase #4 $241.37   9.279%   $263.7667   $263.77   $263.75   $263.80  
  Purchase #5 $89.43   13.850%   $101.8161   $101.82   $101.80   $101.80  
  Purchase #6 $181.63   6.372%   $193.2035   $193.20   $193.20   $193.20  
  Purchase #7 $221.66   5.751%   $234.4077   $234.41   $234.40   $234.40  
  7 purchase totals = $1,088.49       $1,171.9009   $1,171.90   $1,171.85   $1,171.80