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 $60.93   12.704%   $68.6705   $68.67   $68.65   $68.70  
  Purchase #2 $29.66   13.137%   $33.5564   $33.56   $33.55   $33.60  
  Purchase #3 $153.72   13.195%   $174.0034   $174.00   $174.00   $174.00  
  Purchase #4 $85.84   13.178%   $97.152   $97.15   $97.15   $97.20  
  Purchase #5 $210.57   11.571%   $234.9351   $234.94   $234.95   $234.90  
  Purchase #6 $207.68   8.721%   $225.7918   $225.79   $225.80   $225.80  
  Purchase #7 $203.96   7.753%   $219.773   $219.77   $219.75   $219.80  
  7 purchase totals = $952.36       $1,053.8822   $1,053.88   $1,053.85   $1,054.00