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 $91.44   4.737%   $95.7715   $95.77   $95.75   $95.80  
  Purchase #2 $193.45   7.122%   $207.2275   $207.23   $207.25   $207.20  
  Purchase #3 $24.52   5.208%   $25.797   $25.80   $25.80   $25.80  
  Purchase #4 $93.85   12.417%   $105.5034   $105.50   $105.50   $105.50  
  Purchase #5 $160.30   8.744%   $174.3166   $174.32   $174.30   $174.30  
  Purchase #6 $43.75   10.499%   $48.3433   $48.34   $48.35   $48.30  
  Purchase #7 $204.43   5.821%   $216.3299   $216.33   $216.35   $216.30  
  7 purchase totals = $811.74       $873.2892   $873.29   $873.30   $873.20