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 $174.39   13.180%   $197.3746   $197.37   $197.35   $197.40  
  Purchase #2 $153.79   13.545%   $174.6209   $174.62   $174.60   $174.60  
  Purchase #3 $143.57   5.858%   $151.9803   $151.98   $152.00   $152.00  
  Purchase #4 $225.49   5.814%   $238.6   $238.60   $238.60   $238.60  
  Purchase #5 $38.65   6.383%   $41.117   $41.12   $41.10   $41.10  
  Purchase #6 $70.51   5.409%   $74.3239   $74.32   $74.30   $74.30  
  Purchase #7 $37.71   4.133%   $39.2686   $39.27   $39.25   $39.30  
  7 purchase totals = $844.11       $917.2853   $917.28   $917.20   $917.30