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 $148.37   12.202%   $166.4741   $166.47   $166.45   $166.50  
  Purchase #2 $203.47   3.377%   $210.3412   $210.34   $210.35   $210.30  
  Purchase #3 $156.47   4.534%   $163.5643   $163.56   $163.55   $163.60  
  Purchase #4 $65.38   3.512%   $67.6761   $67.68   $67.70   $67.70  
  Purchase #5 $231.36   12.667%   $260.6664   $260.67   $260.65   $260.70  
  Purchase #6 $24.84   3.232%   $25.6428   $25.64   $25.65   $25.60  
  Purchase #7 $156.47   3.276%   $161.596   $161.60   $161.60   $161.60  
  7 purchase totals = $986.36       $1,055.9609   $1,055.96   $1,055.95   $1,056.00