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 $84.89   8.758%   $92.3247   $92.32   $92.30   $92.30  
  Purchase #2 $61.53   11.870%   $68.8336   $68.83   $68.85   $68.80  
  Purchase #3 $113.82   6.415%   $121.1216   $121.12   $121.10   $121.10  
  Purchase #4 $216.79   13.867%   $246.8523   $246.85   $246.85   $246.90  
  Purchase #5 $111.74   11.723%   $124.8393   $124.84   $124.85   $124.80  
  Purchase #6 $115.89   4.379%   $120.9648   $120.96   $120.95   $121.00  
  Purchase #7 $211.42   6.492%   $225.1454   $225.15   $225.15   $225.10  
  7 purchase totals = $916.08       $1,000.0817   $1,000.07   $1,000.05   $1,000.00