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 $156.76   12.264%   $175.985   $175.99   $176.00   $176.00  
  Purchase #2 $60.84   3.862%   $63.1896   $63.19   $63.20   $63.20  
  Purchase #3 $153.38   11.174%   $170.5187   $170.52   $170.50   $170.50  
  Purchase #4 $238.86   6.178%   $253.6168   $253.62   $253.60   $253.60  
  Purchase #5 $106.26   11.535%   $118.5171   $118.52   $118.50   $118.50  
  Purchase #6 $90.66   3.214%   $93.5738   $93.57   $93.55   $93.60  
  Purchase #7 $102.68   7.118%   $109.9888   $109.99   $110.00   $110.00  
  7 purchase totals = $909.44       $985.3898   $985.40   $985.35   $985.40