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 $157.84   10.219%   $173.9697   $173.97   $173.95   $174.00  
  Purchase #2 $178.29   4.728%   $186.7196   $186.72   $186.70   $186.70  
  Purchase #3 $231.29   4.584%   $241.8923   $241.89   $241.90   $241.90  
  Purchase #4 $13.78   6.832%   $14.7214   $14.72   $14.70   $14.70  
  Purchase #5 $27.55   3.570%   $28.5335   $28.53   $28.55   $28.50  
  Purchase #6 $137.66   9.111%   $150.2022   $150.20   $150.20   $150.20  
  Purchase #7 $60.77   7.829%   $65.5277   $65.53   $65.55   $65.50  
  7 purchase totals = $807.18       $861.5664   $861.56   $861.55   $861.50