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 $248.67   5.413%   $262.1305   $262.13   $262.15   $262.10  
  Purchase #2 $58.78   11.660%   $65.6337   $65.63   $65.65   $65.60  
  Purchase #3 $111.98   3.749%   $116.1781   $116.18   $116.20   $116.20  
  Purchase #4 $131.41   5.129%   $138.15   $138.15   $138.15   $138.20  
  Purchase #5 $73.65   3.142%   $75.9641   $75.96   $75.95   $76.00  
  Purchase #6 $238.41   12.852%   $269.0505   $269.05   $269.05   $269.10  
  Purchase #7 $68.70   8.251%   $74.3684   $74.37   $74.35   $74.40  
  7 purchase totals = $931.60       $1,001.4753   $1,001.47   $1,001.50   $1,001.60