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 $158.39   13.441%   $179.6792   $179.68   $179.70   $179.70  
  Purchase #2 $33.38   3.467%   $34.5373   $34.54   $34.55   $34.50  
  Purchase #3 $125.55   5.588%   $132.5657   $132.57   $132.55   $132.60  
  Purchase #4 $144.74   5.252%   $152.3417   $152.34   $152.35   $152.30  
  Purchase #5 $207.81   5.481%   $219.2001   $219.20   $219.20   $219.20  
  Purchase #6 $141.25   6.650%   $150.6431   $150.64   $150.65   $150.60  
  Purchase #7 $184.59   13.459%   $209.434   $209.43   $209.45   $209.40  
  7 purchase totals = $995.71       $1,078.4011   $1,078.40   $1,078.45   $1,078.30