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 $49.75   7.133%   $53.2987   $53.30   $53.30   $53.30  
  Purchase #2 $119.92   4.160%   $124.9087   $124.91   $124.90   $124.90  
  Purchase #3 $204.35   3.755%   $212.0233   $212.02   $212.00   $212.00  
  Purchase #4 $150.74   12.550%   $169.6579   $169.66   $169.65   $169.70  
  Purchase #5 $174.95   8.377%   $189.6056   $189.61   $189.60   $189.60  
  Purchase #6 $80.82   11.544%   $90.1499   $90.15   $90.15   $90.10  
  Purchase #7 $186.62   8.242%   $202.0012   $202.00   $202.00   $202.00  
  7 purchase totals = $967.15       $1,041.6453   $1,041.65   $1,041.60   $1,041.60