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 $46.27   11.346%   $51.5198   $51.52   $51.50   $51.50  
  Purchase #2 $204.42   9.313%   $223.4576   $223.46   $223.45   $223.50  
  Purchase #3 $156.60   9.615%   $171.6571   $171.66   $171.65   $171.70  
  Purchase #4 $181.81   7.444%   $195.3439   $195.34   $195.35   $195.30  
  Purchase #5 $173.37   10.370%   $191.3485   $191.35   $191.35   $191.30  
  Purchase #6 $198.62   9.536%   $217.5604   $217.56   $217.55   $217.60  
  Purchase #7 $7.77   3.503%   $8.0422   $8.04   $8.05   $8.00  
  7 purchase totals = $968.86       $1,058.9295   $1,058.93   $1,058.90   $1,058.90