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 $106.79   6.366%   $113.5883   $113.59   $113.60   $113.60  
  Purchase #2 $228.54   12.580%   $257.2903   $257.29   $257.30   $257.30  
  Purchase #3 $25.99   11.604%   $29.0059   $29.01   $29.00   $29.00  
  Purchase #4 $46.44   9.107%   $50.6693   $50.67   $50.65   $50.70  
  Purchase #5 $229.81   9.403%   $251.419   $251.42   $251.40   $251.40  
  Purchase #6 $225.58   12.816%   $254.4903   $254.49   $254.50   $254.50  
  Purchase #7 $58.91   6.220%   $62.5742   $62.57   $62.55   $62.60  
  7 purchase totals = $922.06       $1,019.0373   $1,019.04   $1,019.00   $1,019.10