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 $50.53   12.121%   $56.6547   $56.65   $56.65   $56.70  
  Purchase #2 $169.73   6.377%   $180.5537   $180.55   $180.55   $180.60  
  Purchase #3 $184.99   8.461%   $200.642   $200.64   $200.65   $200.60  
  Purchase #4 $194.79   12.375%   $218.8953   $218.90   $218.90   $218.90  
  Purchase #5 $133.61   11.429%   $148.8803   $148.88   $148.90   $148.90  
  Purchase #6 $147.55   13.147%   $166.9484   $166.95   $166.95   $166.90  
  Purchase #7 $88.68   8.249%   $95.9952   $96.00   $96.00   $96.00  
  7 purchase totals = $969.88       $1,068.5696   $1,068.57   $1,068.60   $1,068.60