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 $61.95   13.179%   $70.1144   $70.11   $70.10   $70.10  
  Purchase #2 $218.77   9.639%   $239.8572   $239.86   $239.85   $239.90  
  Purchase #3 $207.39   10.267%   $228.6827   $228.68   $228.70   $228.70  
  Purchase #4 $241.42   11.763%   $269.8182   $269.82   $269.80   $269.80  
  Purchase #5 $75.45   3.142%   $77.8206   $77.82   $77.80   $77.80  
  Purchase #6 $115.61   9.424%   $126.5051   $126.51   $126.50   $126.50  
  Purchase #7 $132.95   12.113%   $149.0542   $149.05   $149.05   $149.10  
  7 purchase totals = $1,053.54       $1,161.8524   $1,161.85   $1,161.80   $1,161.90