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 $158.51   11.325%   $176.4613   $176.46   $176.45   $176.50  
  Purchase #2 $120.96   5.251%   $127.3116   $127.31   $127.30   $127.30  
  Purchase #3 $223.42   9.452%   $244.5377   $244.54   $244.55   $244.50  
  Purchase #4 $197.42   11.713%   $220.5438   $220.54   $220.55   $220.50  
  Purchase #5 $48.70   12.475%   $54.7753   $54.78   $54.80   $54.80  
  Purchase #6 $70.27   5.736%   $74.3007   $74.30   $74.30   $74.30  
  Purchase #7 $165.32   5.674%   $174.7003   $174.70   $174.70   $174.70  
  7 purchase totals = $984.60       $1,072.6307   $1,072.63   $1,072.65   $1,072.60