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 $63.31   11.796%   $70.778   $70.78   $70.80   $70.80  
  Purchase #2 $53.65   12.141%   $60.1636   $60.16   $60.15   $60.20  
  Purchase #3 $168.52   3.467%   $174.3626   $174.36   $174.35   $174.40  
  Purchase #4 $232.33   9.658%   $254.7684   $254.77   $254.75   $254.80  
  Purchase #5 $150.81   12.831%   $170.1604   $170.16   $170.15   $170.20  
  Purchase #6 $103.90   3.180%   $107.204   $107.20   $107.20   $107.20  
  Purchase #7 $217.37   6.226%   $230.9035   $230.90   $230.90   $230.90  
  7 purchase totals = $989.89       $1,068.3405   $1,068.33   $1,068.30   $1,068.50